NET2890 datasheet(24/73 Pages) ETC

24 / 73 page

Specification

NET2890 USB Interface Controller

____________________________________________________________________________________

NetChip Technology, Inc., 1999

335 Pioneer Way, Mountain View, California 94041

TEL (650) 526-1490

FAX (650) 526-1494

http://www.netchip.com

Rev 2.0, Draft 9, July 16, 1999

4.5.3.2 Isochronous In Transactions

Isochronous In endpoints are used to transfer data from the NET2890 local bus to a USB host. An

isochronous IN transaction consists of the following:

Stage

Packet Contents

# of

bytes

Source

IN Token

IN PID, address, endpoint, and CRC5

Host

Data

DATA0 PID, N data bytes, and CRC16

N+3

NET2890

The USB host initiates an Isochronous IN transaction by sending an IN token to an Isochronous IN

endpoint. The Data IN Token Interrupt status bit is set when the IN token is recognized. If this interrupt

is enabled, the local interrupt IRQ# pin is asserted. If there is data in the endpoint’s FIFO, it is returned to

the host. If the endpoint has no data to return, a zero length packet is returned to the host. The NET2890

responds to the IN token according to the following table.

FIFO

Valid

Mode

FIFO

Valid

Bit

End of

Transfer

Response Bit

Size of

Packet

Amount of Data in

FIFO

Action

empty

Zero length packet to host;

USB IN NAK Sent status

bit set

Maximum

empty

Zero length packet to host

< Maximum

empty

Zero length packet to host;

USB IN NAK Sent status

bit set

empty

Zero length packet to host

Return data to host

< Max Packet Length

Zero length packet to host;

USB IN NAK Sent status

bit set

>= Max Packet Length

Return data to host

empty

Zero length packet to host

Return data to host

After the packet has been sent to the host, the Data Packet Transmitted Interrupt status bit is set. If this

interrupt is enabled, the local interrupt IRQ# pin is asserted. No handshake packets are returned to the host,

but the USB IN ACK Sent, USB IN NAK Sent, and Timeout status bits are still set to indicate the status

of the transaction. After every data packet is transmitted, the local CPU should sample these status bits to

determine if the packet was successfully transmitted to the host.

By definition, isochronous endpoints do not utilize handshaking with the host. Since there is no way to

return a stall acknowledge from an isochronous endpoint to the host, data which is sent to a stalled

isochronous endpoint will be received normally.

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